Inspection of wafers, both for defects in wafer features and to confirm that the features conform to specified parameters, is an integral part of the wafer fabrication process. One of the methods known in the art for performing such an inspection uses an opto-thermal pump/probe technique. In this technique a first optical source (the pump) heats a location of the wafer, and a second optical source (the probe) investigates the effect of the heating to determine a property of the location, such as its resistance. U.S. Pat. No. 6,971,791, to Borden et al., whose disclosure is incorporated herein by reference, describes a method for identifying defects in a conductive structure of a wafer. The method is based on measurements of the heat transfer through the conductive structure.
U.S. Pat. No. 7,136,163, to Borden et al., whose disclosure is incorporated herein by reference, describes evaluation of a semiconductor wafer having two regions with different dopant concentration profiles. The evaluation performs measurements indicative of a difference in reflectivity between the regions.
U.S. Pat. No. 7,133,128, to Clarysse, et al., whose disclosure is incorporated herein by reference, describes determining the dopant profile of doped regions in a semiconductor substrate by using a pump laser to create excess carriers in the semiconductor substrate.